Generally, as a semiconductor light emitting device, a LED (Light Emitting Diode) can be included, which is a device used for converting electrical signals in the form of infrared, visible and ultraviolet light to emit light by using the characteristics of compound semiconductor.
As for the range of use of LEDs, LEDs are usually used for home appliances, remote controllers, electric signs, displays, a variety of automation equipment, etc., and roughly divided into IRED (Infrared Emitting Diode) and VLED (Visible Light Emitting Diode). The structure of the above-said LED is as follows in general.
Generally, in a blue LED, a N type GaN layer is formed on a sapphire substrate, N-metal is formed on one side of the surface of the N type GaN layer, and an active layer is formed on the portions except for the region where the N-metal is formed. And, a P type GaN layer is formed on the active layer, and P-metal is formed on the P type GaN layer. The active layer is a layer that generates light by holes flowing through the P-metal and electrons flowing through the N-metal being combined to each other.
The aforementioned LED is used for home appliances, electric signs and the like according to the intensity of light output. Especially, LEDs have a tendency to become slimmer as information communication equipment are getting smaller in size, and peripheral equipment, such as resistors, condensers, noise filters, etc., are getting much smaller.
Consequently, light emitting devices are packaged in a surface mount device (hereinafter, “SMD”) type so that the light emitting device can be directly mounted to a PCB (Printed Circuit Board). Accordingly, LED lamps used as a display device are also being developed in a SMD type.
Such a SMD can substitute an existing simple lighting lamp, and used for lighting displays, character displays, image displays, etc. that produces variety of colors.
As above, as the range of use of LEDs has been becoming wider, a required luminescence is becoming higher and higher, like in lamps used for daily life, rescue signaling lamps and the like. Thus, high output LEDs have been widely used in recent years.
FIG. 1 is an explosive perspective view of a structure of a light emitting device package according to the prior art.
As shown therein, in the structure of the light emitting device package 100 according to the prior art, electrode lead frames 130 for applying power to a light emitting device from an external PCB are respectively formed and arranged on a package body 120.
A lens 110 is attached on top of the package body 120 in order to improve the light efficiency of light generated from a LED 140 used as the light emitting device.
An assembly having the LED 140 mounted therein is combined to the bottom of the package body 120. Firstly, a reflecting cup 160 with a high light reflectivity is combined onto an electrical conductor 170. The LED 140 is mounted on a sub mount 150 formed of silicon by flip chip bonding or wire bonding. Though not shown, a reflecting hole is formed inside the sub mount by etching the sub mount 150, a reflective layer is formed on the reflecting hole, and then the LED 140 is mounted.
When the LED 140 is mounted on the sub mount 150, the sub mount 150 is mounted on the reflecting cup 160 formed on the conductor 170, and then an electrical connection process with the electrode lead frames 130 of the LED body 120 is carried out so as to apply power.
The light emitting device package 100 thus assembled reflects the light generated from the LED 140 against the reflecting cup 160, and then diffuses the light to outside via the lens 110.
FIG. 2 is a view showing light emitting device packages 100a, 100b and 100c according to the prior art provided in plural number on a circuit substrate 200.
According to FIG. 2, unlike the light emitting device package presented in FIG. 1, a plurality of LEDs 100a, 100b and 100c are used integrally, in which they are provided in three colors of red, green and blue, respectively and lead frames 130a, 130b and 130c are respectively bonded onto the circuit substrate 200 by a solder 180.
However, the light emitting device package 100 having the aforementioned structure has a problem that if the intensity of current is increased in order to obtain light having a high output, a high temperature heat is generated due to poor heat radiation performance in the package. In a case where the high temperature heat exists in the package without being radiated, the resistance becomes very high and thus the light efficiency becomes deteriorated.
Further, the prior art light emitting device package 100 has a drawback that because the conductor 170, reflecting cup 160, package body 120 and the like are separated from each other, the heat generated from the LED is not easily transferred to outside due to a high heat resistance of their contact portions.
Further, there is an inconvenience that since only one LED is mounted in the package body 120, three light emitting device packages must be placed in a set in order to display high output white. In this case, there is another drawback that the control circuit becomes complex and the volume becomes larger.
Further, in the plurality of single unit type light emitting device packages 100a, 100b and 100c combined to each other, the surface area of the entire substrate 200 is increased so as to connect electrodes from outside, thus increasing the cost of the assembling process.
Further, the structure of the prior art light emitting device package 100 has a problem not only in terms of heat radiation but also in terms of structure. Specifically, there is a problem that colors cannot be mixed on an ideal point light source due to the characteristics of RGB color mixing since air bubbles may be formed upon molding and the single unit type light emitting device packages are arranged on a wide surface area. Besides, there is a problem that the thickness of the lens to be mounted becomes larger due to the arrangement of an electrode, insulating layer, molding space and LED.